Thank you for posting, very interesting! However what is not clear to be me is why this high near nucleus activity isn t manifested in the total coma

Message 2 of 16
, Oct 1, 2012

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Thank you for posting, very interesting! However what is not clear to be me is why this high near nucleus activity isn't manifested in the total coma brightness?

Terry

--- In comets-ml@yahoogroups.com, "Nick Howes - FT Project" <howesnickhowes@...> wrote:
>
> Dear group.
>
> It seems that C/2012 S1 (ISON) is potentially going to be rather special, and for several reasons.
>
> We just updated our blog with a few thoughts and some new data on it, and we'll be monitoring this very interesting body with Faulkes continually.
>
> http://bit.ly/QSjMXJ
> With kind regards,and thanks.
>
> Nick Howes, Giovanni Sostero and Ernesto Guido
>

Jakub Cerny

Hi Terry, I think that the problem is when you comparing activity throughout dust filling factor in selected area (ie 16000 km around nucleus) better angular

Message 3 of 16
, Oct 1, 2012

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Hi Terry,

I think that the problem is when you comparing activity throughout dust
filling factor in selected area (ie 16000 km around nucleus) better
angular resolution gives you more precise values, therefore smaller one
will mix larger area and the resulting number will be much smaller. I
think the main message here is that the real activity of comet looks
larger now when its compared to another comets in similar distance.
However I am not sure if this also mean that comet can be brighter in
maximum or it is only interesting physical fact.

Thanks for the link to your interesting blog on this comet. I have a question. The image your show – being a stack of 13 x 2min exposures, shows the

Message 4 of 16
, Oct 2, 2012

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Thanks for the link to your interesting blog on this comet.

I have a question. The image your show – being a stack of 13 x 2min exposures, shows the _diameter_ of the comet’s coma as being at most 5.0” (using the scale on the image). That is, the coma is shown for a radius of no more than 3.0 arc secs from the comet’s nucleus.

Given this, I don’t understand how you can make assertions about activity at greater distances, as would seem to be explicit in your blog statement:
“This behaviour seems to indicate a steep photometric variation along the coma's profile, with a significant increase of the afrho values close to the central condensation (i.e. within about 6" to 8" of the nucleus), which would not be detected using average amateur telescope, for reasons of resolution and seeing conditions.”

Similarly, the distance scale of the comet (at 6.4AU) is roughly 1” = 4000km. So your afrho plot is extending out to about 12 arc secs from the nucleus – far far greater than the evident size of the coma on the image. My simplistic interpretation of the image would suggest that anything on the afrho plot for distances greater than 10,000km was noise-related rather than the comet.

Obviously I’m missing something – and I would appreciate some education on the issue.

Hi Terry Speaking to Giovanni this morning, we re thinking that the key here is about the meaning of the word activity . Our afrho data indicates that in this

Message 5 of 16
, Oct 2, 2012

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Hi Terry

Speaking to Giovanni this morning, we're thinking that the key here is about the meaning of the word "activity". Our afrho data
indicates that in this comet, the near-nucleus abundance of dust is higher compared to the external parts of the coma (under these circumstances, it's a sort of relative "activity" index within the coma itself). This type of behaviour has been
observed in a number of comets and its cause might be due to a number of reasons
(e.g. sublimating grain cloud surrounding the cometary nucleus as is
suspected in several comets). On the other hand, an indication of a high
near-nucleus activity that's feeding of dust in the rest of the coma, may be explained by the reported total brightness of C/2012 S1 (which is already
pretty high, if you consider its current distance from the Sun).

More study is needed though

--- In comets-ml@yahoogroups.com, "terryjlovejoy" <terryjlovejoy@...> wrote:
>
> Thank you for posting, very interesting! However what is not clear to be me is why this high near nucleus activity isn't manifested in the total coma brightness?
>
> Terry
>
> --- In comets-ml@yahoogroups.com, "Nick Howes - FT Project" <howesnickhowes@> wrote:
> >
> > Dear group.
> >
> > It seems that C/2012 S1 (ISON) is potentially going to be rather special, and for several reasons.
> >
> > We just updated our blog with a few thoughts and some new data on it, and we'll be monitoring this very interesting body with Faulkes continually.
> >
> > http://bit.ly/QSjMXJ
> > With kind regards,and thanks.
> >
> > Nick Howes, Giovanni Sostero and Ernesto Guido
> >
>

gvnn64@libero.it

Hi Dave, IMHO the rendition of a JPG picture isn t accurate enough to extrapolate any reliable parameter, included the coma size: depending on the image

Message 6 of 16
, Oct 2, 2012

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Hi Dave,
IMHO the rendition of a JPG picture isn't accurate enough to extrapolate any reliable parameter, included the coma size: depending on the image processing parameters, compression, etc. you can enhance the apparent coma size, or reduce it, depending on what you want to show.

We do know that, currently, this comet has an actual coma size of about 9"x11": this is reported in IAUC 3238, and actually it's clearly visible Majdanak's stacking (BTW I hope that Artyom or Vitaly will post it soon or later, because it shows pretty well the current shape of the comet).

On the other hand, you can easily understand where the coma physically ends, directly from the afrho data: on the graph, it's the flex (minimum value of afrho of about 900cm) having a radius of nearly 31,000 km. These 31,000 Km distance from the nucleus, roughly correspond to a radius of about 6" (then not far from the 11" visible in Majdanak's image). The afrho algorithm is very sentitive in this. Any data in the panel further away from these 31,000 Km, is "noise". We didn't cut the graph at the 31,000 Km limit, just to show such flex, so people might realize were the sky background actually starts (obviously in any scientific publication, we will report only meaningful data).

Hope that this was helpful to clarify the situation.

Bye,
Giovanni

buzzlyr2001

I hope someone can confirm this image of C/2012 S1 (ISON). Taken earlier today with FT (North) remotely from the Norman Lockyer Observatory. Image taken

Confirmed with 100% certainty. Now Giovanni et al. can use the FITS images
to update the Afrho data.

Richard Miles
BAA

David Strange

Richard, I had a problem accessing the FITS data yesterday. Only 75% of the image was apparent when downloaded. My images were captured jpg s from our FTN

Message 11 of 16
, Oct 5, 2012

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Richard,

I had a problem accessing the FITS data
yesterday. Only 75% of the image was apparent when downloaded.
My images were captured jpg's from our FTN image
archive page. Could you take a look at the FITS data please?
Thanks
David